(1) Field of the Invention
The present invention relates to ferromagnetic Ni3FeN which is epitaxial. In particular the present invention relates to a process for preparing the epitaxial Ni3FeN.
(2) Background of the Invention
The need for improvements in sensitivity, performance, and reduction in size of magnetoresistive devices, such as non-volatile magnetoresistive random access memory (MRAM) and magnetic sensors, is the driving force in searching for new magnetic materials. The magnetic switching characteristics of patterned ferromagnetic films used in nanostructure magnetoresistive devices such as MRAM and magnetic sensors are critical to the sensitivity and performance of these generations of magnetic devices (Zheng, Y., et al., Appl. Phys. 85 4776 (1999)). The homogeneity of magnetic domains, magnetic anisotropy and magnetic domain reversal speed (switching speed) are some of the critical factors in the sensitivity and performance of the mentioned devices.
In recent years, non-epitaxial Permalloy is one of the favored ferromagnetic materials that has been used in fabrication of read/write head, MRAM (magnetic tunnel junction (MTJ) structure), and other magnetic storage element and magnetic sensors. Non-epitaxial Permalloy (Py) is one of the particular types of the Fe—Ni alloy family, with a nickel concentration of 81%, (Ni81Fe19), and is an fcc derivative L12 structure “soft” ferromagnetic metal which is easily magnetized and demagnetized. The magnetic and transport properties of non-epitaxial Py thin films has been studied and used in different devices in great depth. One advantage of using non-epitaxial Py (with respect to other ferromagnets such as Co and Fe) in magnetic devices is its softness. Unfortunately, non-epitaxial Py thin films can have single-magnetic-domain state only for sub-micrometer in-plane dimensions of a certain shape.
It has been shown that by introducing nitrogen as an interstitial impurity into a ferromagnetic metal, which results in expansion of the host lattice, the magnetic, transport and structural properties of the host materials will change. In the past few decades, several investigators have studied numerous of magnetic materials such as 3d metallic and 3d-3f intermetallic compounds. Most of the reported works were focused on iron nitrides (Loloee, R., et al., Appl. Phys. Lett, 82 3281 (2003)), nitrodes of 3d-4f intermetallic compounds, and a few on Fe—Ni nitride systems (Panda, R. N., et al., J. Appl. Phys., 86 3295 (1999); Li, F., et al., Appl. Phys. Lett., 66 2343(1995); and Wang, H. Y., et al., J. Appl. Phys. 91 1453 (2002)). See also Loloee, R., et al, Philosophical Magazine 81 261-273(2001) and Mohn et al, Physical Review B 45, No. 8 (1992), all of which are incorporated by reference.
In general, insertion of interstitial nitrogen into the NiFe unit cell allows the structure of non-epitaxial Ni3FeN to remain cubic (fcc-like) with Ni atoms at fcc sites, Fe atoms at the corner of the unit cell and the interstitial nitrogen atom at body center. The structure and/or magnetic properties of (Fe1-xNix)4N compounds with various X between 0 and 0.6 and the nanocrystalline γ-Fe—Ni—N system (X 0.75) have been studied by several investigators (Panda, R. N., et al., J. Appl. Phys., 86 3295 (1999); Li, F., et al., Appl. Phys. Lett., 66 2343(1995); and Wang, H. Y., et al., J. Appl. Phys. 91 1453 (2002)), all of which are incorporated by reference.
The state of the patent art in ferromagnetic devices is shown in U.S. Pat. Nos. 5,264,981 to Campbell et al., 6,473,960 to Schwartz et al., 6,495,311 and 6,667,850 to Khan et al., which are all incorporated by reference herein. Other references are JOM-e 52(6) 2000 and Caruso et al., Sensors Mag. 